1. Field of the Invention
The present invention relates to an electron beam writing method and a fine pattern writing system for writing a fine pattern according to a desired uneven pattern when manufacturing an imprint mold, magnetic transfer master substrate, or the like for a high density magnetic recording medium, such as a discrete track medium, bit pattern medium, or the like.
The invention also relates to a method for manufacturing an uneven pattern carrying substrate, including an imprint mold, magnetic transfer master substrate or the like, having an uneven pattern surface formed through a writing step performed by the electron beam writing method described above. The invention further relates to a method for manufacturing a magnetic disk medium having an uneven pattern transferred thereto from the uneven pattern carrying substrate or imprint mold, and a method for manufacturing a magnetic disk medium having a magnetized pattern transferred thereto from the magnetic transfer master substrate.
2. Description of the Related Art
Generally, information patterns, such as servo patterns and the like are formed on current magnetic disk media. In view of the demand of higher recording density, a discrete track medium (DTM) in which magnetic interference between adjacent data tracks is reduced by separating the tracks with a groove pattern (guard band) has been attracting wide attention. A bit pattern medium (BPM) proposed for achieving still higher density is a medium in which magnetic substances forming single magnetic domains (single-domain particles) are physically isolated and disposed regularly, and one bit is recorded in one particle.
Heretofore, fine patterns, such as servo patterns and the like, have been formed on magnetic media by uneven patterns, magnetic patterns, or the like and an electron beam writing method for patterning a predetermined fine pattern on a master of a magnetic transfer master substrate or the like has been proposed. In the electron beam writing method, a pattern is written on a substrate applied with a resist by irradiating thereon an electron beam corresponding to the shape of the pattern while rotating the substrate as described, for example, in U.S. Pat. No. 7,026,098 and Japanese Unexamined Patent Publication No. 2006-184924.
The electron beam writing method described in U.S. Pat. No. 7,026,098 is a method in which when, for example, writing a rectangular or parallelogram element constituting a servo pattern extending in a tack width direction, the electron beam is deflected in a radial direction while being vibrated rapidly in a circumferential direction, thereby scanning the beam so as to completely fill the area of the element.
The electron beam writing method described in Japanese Unexamined Patent Publication No. 2006-184924 is a method in which the electron beam is vibrated back and forth in a track width direction of the pattern.
In the mean time, in the electron beam writing methods described above, a pattern shape actually exposed on a resist differs from that written on the substrate by scanning an electron beam due to proximity effect, which depends on the element density of a fine pattern and the exposed shape in a high element density area becomes larger than the written shape, and it is known that it is necessary to perform a proximity-effect correction in which the amount of dose (irradiation dose) is changed.
The proximity effect in the electron beam writing described above is exposure effect to an adjacent writing area due to scattering of the irradiated electron beam, and the impact on a writing pattern varies with the element density of the pattern. That is, when an electron beam is incident on a resist, the beam is broadened by forward scattering as it propagates in the resist toward the substrate. Further, the beam incident on the substrate is scattered, causing backward scattering in which the beam is bounced back from the bottom of the substrate with a large scattering angle. The proximity effect is caused by the fact that the resist is exposed broader than the beam irradiation area by the scattered electrons.
The fine pattern described above is an aggregation of elements, each corresponding to each recording signal, and in a densely arranged region where elements are proximally arranged successively as in the central portion of the aggregation of element arrangement, the proximity effect becomes large due to many scattered electrons involving in the writing of adjacent elements and the amount of dose tends to be excessive. On the other hand, in a sparsely arranged region where only a few elements to be written are arranged around as in a contour portion of the aggregation of element arrangement, the number of impacting scattered electrons is small and the proximity effect becomes small, so that the amount of dose tends to be insufficient. These phenomena become more significant as the resist sensitivity is increased.
If the amount of dose varies according to the element density, when a resist after writing exposure is developed, the exposed resist area to be removed differs from the writing area, whereby an error occurs in the element shape, influencing the forming accuracy of a desired pattern.
For example, as illustrated in FIG. 9A, when six elements 3a to 3c having the same signal length (line width) are written on one track by vibrating electron beam EB back and forth in an element width direction (circumferential direction of the substrate), and if the scattering involving in the writing of one element is assumed to influence two elements on each side of the element, the element arrangement density of each of elements 3a on both ends is a sparsely arranged region which is influenced by the two inner elements, that of each of elements 3b located inner side of elements 3a is an intermediately arranged region which is influenced by the one outer element and two inner elements, and that of each of central elements 3c is a densely arranged region which is affected by two elements on each side.
FIG. 9B schematically illustrates an exposed pattern as the result of the electron beam writing shown in FIG. 9A. Where each of elements 4a on both ends has the exposed shape corresponding to the writing width of FIG. 9A from the resist sensitivity and beam intensity, the exposed width of each of elements 4b in the intermediately arranged region becomes larger than the writing width by a predetermined rate, and the exposed width of each of elements 4c in the central densely arranged region becomes further larger than that of elements 4b by a predetermined rate and the element spacing is narrowed. Thus, it is necessary to perform a proximity-effect correction in which the electron beam writing is adjusted for each element so that the actually exposed pattern in FIG. 9B becomes the design pattern shown in FIG. 9A.
The proximity-effect correction in actual electron beam writing has a problem that the setting and write control is complicated.
For example, it is possible to reduce the amplitude of the back and forth vibration of electron beam EB in the circumferential direction in FIG. 9A for the writing of elements 3c so as to be written in narrower lines, whereby a proximity-effect correction may be performed. Fine adjustment of the amplitude for the writing of each element involves changes in the oscillation signal and control difficulties.
In view of the circumstance described above, it is an object of the present invention to provide an electron beam writing method capable of accurately writing a fine pattern, to be formed on a magnetic disk medium, on the entire surface of a substrate in a predetermined manner and rapidly with a constant amount of dose over the entire substrate by enabling an easy proximity-effect correction, and a fine pattern writing system for implementing the electron beam writing method.
It is a further object of the present invention to provide a method for manufacturing an uneven pattern carrying substrate, such as an imprint mold or a magnetic transfer master substrate, having a fine pattern accurately written by an electron beam, and a method for manufacturing a magnetic disk medium using the uneven pattern carrying substrate in which an uneven pattern or a magnetic pattern is transferred from the uneven pattern carrying substrate to the magnetic disk medium.